Relay apparatus, relay method, and relay program

ABSTRACT

A relay apparatus for relaying a packet in radio communication by a wireless terminal in a communication area includes a packet monitoring part for obtaining data on a bandwidth to be used in the radio communication by the wireless terminal from a packet to be relayed, a bandwidth managing part for calculating and recording a total bandwidth in use used for the radio communication by the wireless terminal from the obtained data on a bandwidth, a retransmission adjusting part for determining an upper limit of a packet retransmission number, in accordance with an amount of an available bandwidth obtained by excluding a total bandwidth in use from a maximum bandwidth, and a retransmitting part for retransmitting a packet in a range not exceeding the upper limit of the packet retransmission number. Consequently, the relay apparatus enables retransmission appropriately adaptable to a use situation of a bandwidth by wireless communication of a wireless terminal in a communication area.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a relay apparatus for relaying, in alimited bandwidth, communication by a plurality of wireless terminals ina communication area, for example, as in access points in a wirelesslocal area network (LAN).

2. Description of Related Art

Recently, for example, as in an IP telephone via a wireless LAN, awireless terminal that performs a telephone conversation via radiocommunication has become widespread. The wireless terminal that performsa telephone conversation via radio communication enables a telephoneconversation with a terminal on a partner side by performing radiocommunication with a relay apparatus (e.g., an access point of awireless LAN, etc.). In such a communication form, a plurality ofwireless terminals are present in a communication area of a relayapparatus, whereby simultaneous telephone conversations by the wirelessterminals occur. In this case, the plurality of wireless terminals sharea bandwidth available in the relay apparatus, and perform communicationrespectively.

Furthermore, generally, in radio communication between a wirelessterminal and a relay apparatus, a packet transmission error rate is highdue to the influence by an obstacle and the like. In the case where therelay apparatus fails in the transmission of a packet, it retransmitsthe packet until it succeeds in transmitting the packet. When a packetis retransmitted, a bandwidth in use increases accordingly, and when abandwidth in use exceeds the capacity of transmission which relayapparatus manages, transmissions of radio terminals and relay apparatusinterfere each other, and tend to end in failures. Therefore, the numberof retransmissions should be as small as possible.

Conventionally, a method for preventing the number of retransmissionsfrom increasing excessively in an OFDM-CDMA transmitter is proposed(e.g., see JP 2004-187226 A). According to this method, when the numberof retransmissions increases, the increase in the number ofretransmissions is prevented by increasing the number of sub-carriers ofan OFDM.

However, according to the above-mentioned conventional method, only thecommunication state among individual apparatuses are taken intoconsideration. On the other hand, there is a demand for controlling thenumber of packet retransmissions in accordance with the entire usesituation of a bandwidth by radio communication in a communication area.For example, during a peak time such as the simultaneous telephoneconversations by a number of wireless terminals in a communication area,unless the number of retransmissions in radio communication by onewireless terminal is suppressed in accordance with an availablebandwidth, the available bandwidth may be exhausted due toretransmissions. Consequently, the transmission of communication data ofanother wireless terminal may be delayed. Furthermore, during anoff-peak time in which only one wireless terminal performs communicationin a communication area, in spite of the fact that there is a sufficientavailable bandwidth for retransmissions, retransmissions of a previouslyset upper limit value or more cannot be performed, resulting in a packettransmission failure. According to the above-mentioned conventionalmethod, since the entire use situation of a bandwidth for radiocommunication by wireless terminals in a communication area is not takeninto consideration, the above-mentioned circumstances cannot beprevented.

SUMMARY OF THE INVENTION

Therefore, with the foregoing in mind, it is an object of the presentinvention to provide a relay apparatus, a relay method, and a relayprogram enabling a retransmission appropriately compliant with theentire use situation of a bandwidth for radio communication by wirelessterminals in a communication area.

A relay apparatus according to the present invention for relaying apacket to be transmitted in radio communication by at least one wirelessterminal in a communication area includes: a packet monitoring part forobtaining data on a bandwidth used in the radio communication by thewireless terminal from the packet to be relayed by the relay apparatus;a bandwidth managing part for calculating and recording a totalbandwidth in use used for the radio communication by the wirelessterminal in the communication area based on the data obtained by thepacket monitoring part; a retransmission adjusting part for determiningan upper limit of a packet retransmission number in accordance with anamount of an available bandwidth obtained by excluding the totalbandwidth in use from a maximum bandwidth available in the radiocommunication by the wireless terminal; and a retransmitting part forretransmitting a packet whose transmission has ended in failure by therelay apparatus, in a range not exceeding the upper limit of the packetretransmission number determined by the retransmission adjusting part.

The retransmission adjusting part determines the upper limit of thepacket retransmission number in accordance with the amount of theavailable bandwidth obtained by excluding the total bandwidth in usecalculated based on the data obtained by the packet monitoring part fromthe maximum bandwidth available in the radio communication. Therefore,the upper limit of the number of retransmissions adaptable to the entireuse situation of a bandwidth for the radio communication in thecommunication area is determined. The retransmitting part retransmits apacket whose transmission has ended in failure by the relay apparatusbased on the upper limit of the number of retransmissions determined bythe retransmission adjusting part. Therefore, the retransmissionappropriately adaptable to the entire use situation of a bandwidth canbe performed. Consequently, the communication quality of the radiocommunication by the wireless terminal in the communication area of therelay apparatus can be enhanced.

In the relay apparatus according to the present invention, it ispreferable that the retransmission adjusting part divides the availablebandwidth by the number of wireless terminals that perform the radiocommunication in the communication area to obtain an available bandwidthper wireless terminal, and determines the upper limit of the packetretransmission number for each wireless terminal, using the availablebandwidth per wireless terminal.

According to the above configuration, the upper limit of the number ofretransmissions per wireless terminal is determined by the availablebandwidth per wireless terminal obtained by dividing the entireavailable bandwidth by the number of wireless terminals performing theradio communication. Therefore, one wireless terminal can be preventedfrom repeating retransmissions to use up the available bandwidth.Consequently, the degradation in communication quality at anotherwireless terminal in the communication area can be prevented.Furthermore, in the case where the entire available bandwidth issufficient, the upper limit of the number of retransmissions perwireless terminal increases accordingly, and the possibility of successof packet transmission is increased by retransmitting a packet whosetransmission has ended in failure by the relay apparatus.

In the relay apparatus according to the present invention, it ispreferable that the retransmission adjusting part sets the upper limitof the packet retransmission number by the relay apparatus within aconstant length of time in accordance with the available bandwidth.

By setting the upper limit of the packet retransmission number by therelay apparatus within a constant length of time, the transmission of apacket other than the retransmission packet is ensured within theconstant length of time. Therefore, one wireless terminal can beprevented from repeating retransmissions, thereby allowing a time duringwhich the transmission of a packet other than the retransmission packetcannot be performed to continue for a constant length of time or longer.

In the relay apparatus according to the present invention, it ispreferable that the retransmission adjusting part sets the upper limitof the packet retransmission number for each radio communicationperformed by the wireless terminal. This enables the communicationquality to be adjusted for each radio communication.

It is preferable that the relay apparatus according to the presentinvention further includes a transmission history recording part forrecording a communication identifier for identifying communication ofthe packet to be relayed by the relay apparatus and relationship datathat represents a relationship between a link speed in communicationrepresented by the communication identifier and a packet transmissionsuccess rate, wherein when retransmitting the packet of thecommunication represented by the communication identifier recorded inthe transmission history recording part, the retransmitting part appliesa link speed at which the packet transmission success rate in thecommunication represented by the communication identifier is highestbased on the relationship data, and retransmits the packet based on theapplied link speed.

The retransmitting part retransmits a packet based on the link speed atwhich the packet transmission success rate is highest in thecommunication represented by the communication identifier recorded inthe transmission history recording part. Therefore, the packet can beretransmitted at a link speed at which the possibility of transmissionsuccess in each communication is high.

The relay apparatus according to the present invention further includesa retransmission history recording part for recording relationship datathat represents a relationship between a retransmission timing of apacket retransmitted by the retransmitting part and a packettransmission success rate, wherein the retransmitting part determines aretransmission timing at which the packet transmission success rate ishighest based on the relationship data, and determines a transmissioninterval at which a packet whose transmission has ended in failure bythe relay apparatus based on the determined retransmission timing.

The retransmitting part determines a transmission interval at which apacket is retransmitted based on the retransmission timing at which thepacket transmission success rate is highest, so that the packet can beretransmitted at a transmission interval at which the possibility ofsuccess of transmission is high.

The relay apparatus according to the present invention further includesa packet loss history recording part for recording a history of a packetloss caused by a packet transmission failure of the relay apparatus foreach wireless terminal; and an acceptable information recording part forrecording data that represents a condition of a count of sequentialpacket losses acceptable in the radio communication for each wirelessterminal, wherein the packet monitoring part obtains data thatrepresents a condition of the count of sequential packet lossesacceptable in the radio communication of the wireless terminal from apacket to be relayed by the relay apparatus and records the data in theacceptable information recording part, and the retransmitting partobtains a count of sequential packet losses at a destination wirelessterminal to which a packet is transmitted and result in transmissionfailure from the packet loss history recording part, determines whetheror not count of the sequential packet losses obtained from the packetloss history part corresponds to the condition of the count of thesequential packet losses acceptable in the radio communication of thedestination wireless terminal represented by the data recorded in theacceptable information recording part, and in a case where count of thesequential packet losses obtained from the packet loss history partcorresponds to the condition, discards the packet without retransmittingit.

The packet loss means that transmission and all retransmissions of apacket has ended in failure. In the case where a packet received from awireless terminal contains data that represents the count of thesequential packet losses capable of accepting a packet loss, the datarepresenting the count of sequential packet losses acceptable isrecorded in the acceptable information recording part by the packetmonitoring part. Therefore, the retransmitting part obtains a count ofsequential packet losses of a packet whose transmission has ended infailure from the packet loss history recording part storing the count ofsequential packet losses, and compares the count of sequential packetlosses with the condition of an acceptable count of sequential packetlosses recorded in the acceptable information recording part, therebydetermining the necessity/unnecessity of retransmission can bedetermined. Consequently, the retransmitting part can reduce the numberof retransmissions as a whole by discarding a packet in wirelesscommunication accepting a packet loss without retransmitting it.

It is preferable that the relay apparatus according to the presentinvention further includes a retransmission number sending part fornotifying the wireless terminal of an upper limit of the packetretransmission number determined by the retransmission adjusting part.

According to the above configuration, in the case where the wirelessterminal fails in the transmission of a packet to a relay apparatus, thewireless terminal can retransmit a packet in a range not exceeding anupper limit of the packet retransmission number notified from theretransmission number sending part. Consequently, the wireless terminalcan retransmit a packet with the number of retransmissions in accordancewith the use situation of a bandwidth in the communication area.

It is preferable that the relay apparatus according to the presentinvention further includes a prioritized communication recording partfor recording a prioritized communication identifier that representsprioritized communication through which the relay apparatus relays apacket by priority; and a priority control part for sending the packetin the prioritized communication represented by the prioritizedcommunication identifier by priority, wherein the retransmissionadjusting part determines an upper limit of a packet retransmissionnumber, in accordance with an amount of an available bandwidth obtainedby excluding the total bandwidth in use from the maximum bandwidthavailable in the radio communication of the relay apparatus, only withrespect to a packet of the prioritized communication, and theretransmitting part retransmits the packet in the communicationrepresented by the prioritized communication identifier among packetswhose transmissions have ended in failure by the relay apparatus in arange not exceeding the upper limit of the packet retransmission numberdetermined by the retransmission adjusting part, and retransmits apacket in communication other than the prioritized communicationrepresented by the prioritized communication identifier among packetswhose transmissions have ended in failure by the relay apparatus by apredetermined number of times.

According to the above configuration, regarding the prioritizedcommunication in which a packet is relayed by priority by the priorityrelaying part, the packet can be retransmitted in a range not exceedingan upper limit of the packet retransmission number in accordance withthe use situation of a bandwidth, and regarding the non-prioritizedcommunication other than the prioritized communication, the number ofretransmissions corresponding to the previously determined number can beensured. Therefore, in the prioritized communication, the number ofretransmissions is suppressed from increasing to cause the delay due toan insufficient bandwidth. On the other hand, in the non-prioritizedcommunication, although the possibility of the occurrence of a delayincreases compared with the prioritized communication, the number ofretransmissions is ensured, so that the occurrence of a packet loss issuppressed.

A relay method according to the present invention for relaying a packetto be transmitted in radio communication by at least one wirelessterminal in a communication area includes obtaining data on a bandwidthused in the radio communication by the wireless terminal from the packetto be relayed by the relay apparatus; calculating and recording a totalbandwidth in use used for the radio communication by the wirelessterminal in the communication area based on the obtained data;determining an upper limit of a packet retransmission number inaccordance with an amount of an available bandwidth obtained byexcluding the total bandwidth in use from a maximum bandwidth availablein the radio communication by the wireless terminal; and retransmittinga packet whose transmission has ended in failure by the relay apparatus,in a range not exceeding the upper limit of the packet retransmissionnumber.

A relay program according to the present invention causes a relayapparatus including a computer to execute processing of relaying apacket to be transmitted in wireless communication by at least onewireless terminal in a communication area, the relay program causing therelay apparatus to execute packet monitoring processing of obtainingdata on a bandwidth used in radio communication by the wireless terminalfrom the packet to be relayed by the relay apparatus; bandwidthmanagement processing of calculating and recording a total bandwidth inuse used for the radio communication by the wireless terminal in thecommunication area based on the data obtained in the packet monitoringprocessing; retransmission adjustment processing of determining an upperlimit of a packet retransmission number, in accordance with an amount ofan available bandwidth obtained by excluding the total bandwidth in usefrom a maximum bandwidth available in the radio communication by thewireless terminal; and retransmission processing of retransmitting apacket whose transmission has ended in failure by the relay apparatus ina range not exceeding the upper limit of the packet retransmissionnumber determined by the retransmission adjusting processing.

According to the present invention, a relay apparatus, a relay method,and a relay program enabling the retransmission appropriately adaptableto the entire use situation of a bandwidth in radio communication by awireless terminal in a communication area can be provided.

These and other advantages of the present invention will become apparentto those skilled in the art upon reading and understanding the followingdetailed description with reference to the accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram showing a configuration of anentire communication system including APs according to Embodiment 1.

FIG. 2 is a functional block diagram showing a configuration of an APaccording to Embodiment 1.

FIG. 3 is a diagram showing examples of data to be recorded in abandwidth information recording part.

FIG. 4A is a diagram showing an example of data to be recorded in aretransmission number recording part. FIG. 4B is a diagram showingexamples of data on variables r and r_max.

FIG. 5 is a flowchart showing an example of retransmission processing ina retransmitting part in Embodiment 1.

FIG. 6A is a diagram showing data on an upper limit value of the numberof retransmissions in Embodiment 1. FIG. 6B is a diagram showingexamples of data on variables r, r_max, R, and R_max.

FIG. 7 is a flowchart showing an example of processing in which aretransmitting part retransmits data using an upper limit of the numberof retransmissions of each packet and an upper limit of a sum of thenumber of retransmissions during a constant length of time.

FIG. 8A is a diagram showing examples of data on an upper limit value ofthe number of retransmissions in Embodiment 1, and FIG. 8B is a diagramshowing examples of data on variables r and r_max corresponding to eachcommunication identifier.

FIG. 9 is a flowchart showing an example of processing in which theretransmitting part retransmits data using an upper limit of the numberof retransmissions of each packet for each communication, and an upperlimit of a sum of the number of retransmissions during a constant lengthof time.

FIG. 10 is a functional block diagram showing a configuration of an APaccording to Embodiment 2.

FIG. 11 is a functional block diagram showing a configuration of an APaccording to Embodiment 3.

FIG. 12 is a diagram showing examples of data to be recorded in aretransmission history recording part.

FIG. 13 is a flowchart showing an operation example of a retransmittingpart in Embodiment 3.

FIG. 14 is a functional block diagram showing a configuration of an APaccording to Embodiment 4.

FIG. 15 is a diagram showing examples of data recorded in a transmissionhistory recording part.

FIG. 16 is a flowchart showing an operation example of theretransmitting part.

FIG. 17 is a functional block diagram showing a configuration of an APaccording to Embodiment 5.

FIG. 18 is a diagram showing examples of data to be recorded in a packetloss history recording part.

FIG. 19 is a diagram showing examples of data to be recorded in anacceptable information recording part.

FIG. 20 is a flowchart showing an operation example of a retransmittingpart in Embodiment 5.

FIG. 21 is a functional block diagram showing a configuration of an APaccording to Embodiment 6.

FIG. 22A is a diagram showing examples of data recorded in aretransmission number recording part. FIG. 22B is a diagram showingexamples of data on variables used in accordance with the determinationin Op 3 in FIG. 23.

FIG. 23 is a flowchart showing an example of processing in which apriority control part and a retransmitting part retransmit data.

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1

Embodiment 1 is the case where a relay apparatus is a wireless LANaccess point (hereinafter, referred to as an “AP”), as an example. FIG.1 is a functional block diagram showing a configuration of APs accordingto the present embodiment together with a function of an entirecommunication system including the APs. The communication system shownin FIG. 1 enables the communication by wireless IP telephones using awireless LAN, for example.

The communication system shown in FIG. 1 includes an AP 1 a, an AP 1 b,a session initiation protocol (SIP) server 2, and a wired terminal 4that are connected to a wired LAN 6, wireless terminals 3 a, 3 b in acommunication area of the AP 1 a, and wireless terminals 3 c, 3 d in acommunication area of the AP 1 b. The wireless terminals 3 a, 3 b andthe wired terminal 4 have a function of an IP telephone terminal. Thenumber of APs connected to the wired LAN 6 is not limited to two asshown in FIG. 1. Furthermore, the number of wireless terminals that maybe present in each communication area of the AP 1 a and the AP 1 b isnot limited to two. Furthermore, appliances other than the AP 1 a, theAP 1 b, the SIP server 2, and the wired terminal 4 may be connected tothe wired LAN 6.

The SIP server 2 is an example of a communication control server in anIP telephone network, and controls the start, change, and completion ofcommunication by at least two communication terminals among a pluralityof communication terminals including the wireless terminals 3 a-3 d andthe wired terminal 4. The SIP server 2 controls the start, change, andcompletion of communication based on an SIP. For example, the SIP server2 receives a communication start request (invite message) sent from anyof the wireless terminals 3 a-3 d and the wired terminal 4, andgenerates a call between terminals that are going to startcommunication. Furthermore, the SIP server 2 receives a communicationcompletion request (bye message) sent from any of the wireless terminals3 a-3 d and the wired terminal 4, and completes a call between terminalsthat are going to complete communication. The communication control isnot limited to the above-mentioned communication control based on theSIP.

(Configuration of AP)

FIG. 2 is a functional block diagram showing a configuration of the AP 1a. Since the configuration of the AP 1 b shown in FIG. 1 is similar tothat of the AP 1 a shown in FIG. 2, the description thereof will beomitted. The AP 1 a includes a wired LAN interface 11, a packetmonitoring part 12, a wireless LAN interface 13, a bandwidth managingpart 14, a retransmission adjusting part 15, a retransmitting part 16, abandwidth information recording part 17, and a retransmission numberrecording part 18.

Examples of the hardware constituting the AP 1 a include an antenna, amodulation circuit, an amplifier circuit, a demodulation circuit, amicroprocessor, and a recording device. Each function of the wired LANinterface 11, the packet monitoring part 12, the bandwidth managing part14, the retransmission adjusting part 15, and the retransmitting part 16is realized when the microprocessor executes a predetermined program.The function of the wireless LAN interface 13 is realized by, forexample, the antenna, the modulation circuit, the amplifier circuit, thedemodulation circuit, and the microprocessor. Furthermore, the bandwidthinformation recording part 17 and the retransmission number recordingpart 18 are embodied by a recording device such as a semiconductormemory, a magnetic memory, or an optical memory.

The wired LAN interface 11 mediates the exchange of data between the AP1 a and the wired LAN 6 in conformity with the specification of thewired LAN. The wireless LAN interface 13 mediates the wireless exchangeof data between the wireless terminals 3 a, 3 b and the AP 1 a inconformity with the specification of the wireless LAN. The wireless LANinterface 13 and the wired LAN interface 11 relay the communicationbetween the wireless terminals 3 a, 3 b and the wired LAN 6.

The wireless LAN interface 13 exchanges data with the wireless terminals3 a, 3 b on a packet basis. In the case where the transmission of apacket from the AP 1 a to the wireless terminals 3 a, 3 b has ended infailure, the retransmitting part 16 controls the wireless LAN interface13 so as to retransmit a packet repeatedly until it succeeds in thetransmission of the packet. Herein, the number of retransmissions to berepeated is referred to as the number of retransmissions. An upper limitis set to the number of retransmissions, and a packet whose transmissionhas not ended in success even when the number of retransmissions reachesthe upper limit is discarded. Consequently, a loss of packet occurs.

The packet monitoring part 12 obtains data regarding a bandwidth used inradio communication between the wireless terminals 3 a, 3 b and the AP 1a from a packet passing through the wireless LAN interface 13 and apacket passing through the wired LAN interface 11, and passes theobtained data to the bandwidth managing part 14.

The bandwidth managing part 14 calculates a total bandwidth in use,which is used in radio communication by the wireless terminals 3 a, 3 bin the communication area of the AP 1 a, using the data passed from thepacket monitoring part 12, and records the total bandwidth in use in thebandwidth information recording part 17.

The retransmission adjusting part 15 determines an upper limit value ofthe number of packet retransmissions, using the total bandwidth in userecorded in the bandwidth information recording part 17, and records theupper limit value in the retransmission number recording part 18. Theretransmission adjusting part 15 determines an upper limit of the numberof packet retransmissions in accordance with the amount of an availablebandwidth obtained by excluding the total bandwidth in use from amaximum bandwidth available in radio communication of the AP 1 a.

The retransmitting part 16 retransmits a packet whose transmission hasended in failure to the wireless LAN interface 13 in a range notexceeding the upper limit of the number of packet retransmissionsrecorded in the retransmission number recording part 18.

(Detail of Functions of Packet Monitoring Part 12 and Bandwidth ManagingPart 14)

Hereinafter, a specific example of the function will be described, inwhich the packet monitoring part 12 obtains data on a bandwidth from apacket passing through the AP 1 a, and the bandwidth managing part 14records bandwidth information based on the data.

Among the packet passing through the wireless LAN interface 13 and thepacket passing through the wired LAN interface 11, the packet monitoringpart 12 may extract, for example, a call control message ofcommunication whose start, change, completion, and the like arecontrolled by the SIP server 2, and pass the call control message to thebandwidth managing part 14. More specifically, the packet monitoringpart 12 can extract a packet of a communication start request, a packetof a communication completion request, and the like, and pass them tothe bandwidth managing part 14. Because of this, the bandwidth managingpart 14 obtains information on the start and completion of communicationperformed via the AP 1 a. Furthermore, the packet of the communicationstart request contains information (e.g., a codec, a frame rate, etc.)on the bandwidth used in communication to be started, so that thebandwidth managing part 14 can also obtain information on a bandwidth byreceiving the communication start request.

As a specific example, the case will be described in which the packetmonitoring part 12 monitors an SIP packet passing through the wirelessLAN interface and an SIP packet passing through the wired LAN interface11, and passes an invite packet and a bye packet among the SIP packetsto the bandwidth managing part 14.

The invite packet is an example of the packet representing acommunication start request. The invite packet includes, for example,information on an IP address and a port number of a wireless terminalthat is going to start communication, a frame rate, a codec, etc. Whenreceiving the invite packet, the bandwidth managing part 14 recordsinformation contained in the invite packet in the bandwidth informationrecording part 17.

FIG. 3 is a diagram showing examples of data to be recorded in thebandwidth information recording part 17. In the examples shown in FIG.3, a communication identifier, a codec, a frame rate, a bandwidth inuse, a link speed, a priority, and a received signal strength indicator(RSSI) are recorded in a bandwidth management table 21 for eachcommunication. The communication identifier is represented by, forexample, an IP address and a port number of a wireless terminal thatperforms the communication.

When receiving the invite packet, the bandwidth managing part 14 addsand records an IP address and a port number of a wireless terminalincluded in the invite packet, a frame rate, a codec, a priority, and anRSSI in the bandwidth management table 21. Furthermore, the bandwidthmanaging part 14 calculates a bandwidth in use, which is used in thecommunication, from the frame rate and the codec, and records thecalculated bandwidth in use. Furthermore, the bandwidth managing part 14also obtains a link speed of the invite packet from the wireless LANinterface 13 and records it. Thus, in the bandwidth management table 21,information on the bandwidth of communication performed via the AP 1 ais recorded in the mass.

Herein, an example of setting of a priority will be described. Forexample, the SIP server 2 creates a table recording a priority for eachuser ID (telephone number, etc.), determines a priority with referenceto the table when receiving a communication start request from a user,and adds the priority to SDP data of an invite packet to be sent to acommunication partner destination or an external part of the SDP data.The bandwidth managing part 14 receives the invite packet, and recordsthe priority in the bandwidth managing table 21. Furthermore, as anexample different from that determined by the SIP server 2, a settingfile, in which priority information associated with an IP address and aport number may be recorded in the AP 1 a.

Furthermore, since the RSSI is added to the packet transmitted/receivedby the wireless LAN interface 13, the packet monitoring part 12 can readthe RSSI and notify the bandwidth managing part 14 of the RSSI.

When receiving a bye packet for requesting the completion ofcommunication, the bandwidth managing part 14 deletes information oncommunication represented by an IP address and a port number of awireless terminal included in the bye packet from the bandwidthmanagement table 21. Consequently, information only on the communicationthat is currently being performed is recorded in the bandwidthmanagement table 21. Therefore, the bandwidth managing part 14calculates a sum of bandwidth in use of each communication recorded inthe bandwidth management table 21, thereby obtaining a current totalbandwidth in use in the AP 1 a.

Herein, although the case has been described in which the bandwidthmanaging part 14 records information on a bandwidth based on a callcontrol message from the communication control server (herein, the SIPserver 2) of the outside such as an invite packet and a bye packet, thedata to be the base for information on a bandwidth is not limited to acall control message. Hereinafter, data to be the base for informationon a bandwidth and other examples will be described.

For example, the packet monitoring part 12 may extract a real-timetransport protocol (RTP) packet among a packet passing through thewireless LAN interface 13 and a packet passing through a wired LANinterface 11, and pass the packet to the bandwidth managing part 14.Since the RTP packet contains a codec and a time stamp, the bandwidthmanaging part 14 can calculate a bandwidth in use for each communicationbased on these pieces of information.

Furthermore, the packet monitoring part 12 may notify the bandwidthmanaging part 14 of the number and size of packets passing through thewireless LAN interface 13 within a constant length of time, and anaverage link speed within the constant length of time. The bandwidthmanaging part 14 can calculate a bandwidth that is currently being usedin the AP 1 a, based on the notified data.

(Operation Example 1 of Retransmission Adjusting Part 15 andRetransmitting Part 16)

Next, a specific example of the case will be described in which theretransmission adjusting part 15 determines an upper limit value of thenumber of packet retransmissions and retransmits a packet based on theupper limit value.

First, the retransmission adjusting part 15 determines an upper limit ofthe number of retransmissions, using the sum of bandwidths in useobtained in the bandwidth managing part 14. Specifically, theretransmission adjusting part 15 calculates the amount of an availablebandwidth with respect to an available bandwidth obtained by excludingthe total bandwidth in use from the maximum bandwidth that can be usedfor radio communication of the AP 1 a. The amount of the availablebandwidth is divided by the number of communications that are currentlybeing performed via the AP 1 a to obtain an available bandwidth percommunication, and the number of retransmissions per packet isdetermined based on this value. It is assumed that the maximum bandwidththat can be used for radio communication of the AP1 a is, for example,recorded in a recording device such as a memory of the AP 1 a at thetime of shipping of the AP 1 a.

Herein, an example of calculation of determining the number ofretransmissions using the data in the bandwidth management table 21shown in FIG. 3 will be described. The sum (128+128=) “256 kbps” of thebandwidths in use is obtained from the data of the bandwidth managementtable 21. Herein, assuming that the maximum bandwidth that can be usedfor radio communication of the AP 1 a is “1000 kbps”, the retransmissionadjusting part 15 calculates an available bandwidth to be (1000−256=)“744 kbps”. It is understood from the data of the bandwidth managementtable 21 that the number of communications that are being relayed by theAP 1 a is “2”. Therefore, the retransmission adjusting part 15 dividesthe available bandwidth “744 kbps” by the number of communications “2”to obtain an available bandwidth “372 kbps” per communication. Theretransmission adjusting part 15 sets “3” to be the number ofretransmissions, which is obtained by dividing the available bandwidth“372 kbps” per communication by the bandwidth in use “128 kbps” of onecommunication, and rounding off fractions of a decimal point of theobtained number.

Herein, although the bandwidth in use in any communication is “128kbps”, in the case where the bandwidth in use varies depending uponcommunication, it is preferable to calculate the number ofretransmissions for each communication. For example, when the link speedchanges from 11 Mbps to 5.5 Mbps in the communication shown in FIG. 3,the bandwidth in use changes from “128 kbps” to “256 kbps”. In such acase, the number of retransmissions of that communication becomes “1”that is obtained by dividing the available bandwidth “372 kbps” percommunication by the bandwidth in use “256 kbps” of one communication,followed by rounding off fractions of a decimal point of the obtainednumber.

The retransmission adjusting part 15 records the calculated number ofretransmissions in the retransmission number recording part 18. FIG. 4Ais a diagram showing an example of data to be recorded in theretransmission number recording part 18. The retransmission adjustingpart 15 periodically calculates the number of retransmissions at apredetermined time interval, and periodically updates the data of theretransmission number recording part 18. Because of this, the number ofretransmissions is updated in accordance with the change in the usesituation of a bandwidth.

The calculation of an upper limit of the number of retransmissions ofthe retransmission adjusting part 15 is an example, and the datarepresenting the calculation method and the upper limit of the number ofretransmissions is not limited thereto. For example, the upper limit maybe represented by a bandwidth available for retransmission, instead ofthe number of retransmissions as shown in FIG. 4A.

The retransmission adjusting part 15 may determine the number ofretransmissions, further using a priority or an RSSI recorded in thebandwidth management table 21. For example, the retransmission adjustingpart 15 can correct the number of retransmissions calculated asdescribed above in accordance with the priority. In this case, theretransmission adjusting part 15 may add “+1” to the number ofretransmissions of communication with a priority of “1st”, “+0,” to thenumber of retransmissions of communication with a priority of “2nd”, and“−1” to the number of retransmissions of communication with a priorityequal to or lower than “+0”.

Furthermore, an example of the case using the RSSI will be described. Ingeneral, as the RSSI is worse, the number of retransmissions until thetransmission of a packet ends in success tends to increase. Morespecifically, there is a relationship between the RSSI and the number ofretransmissions (referred to as a retransmission expectation number)expected until the transmission of a packet ends in success. Therefore,the retransmission expectation number can be obtained from the RSSI,using this relationship. The retransmission adjusting part 15 may obtainthe retransmission expectation number of each communication from theRSSI of each communication, and calculate the retransmission number ofeach communication based on the retransmission expectation number ofeach communication.

Next, a specific example of the retransmission processing of theretransmitting part 16 will be described. FIG. 5 is a flowchart showingan example of the retransmission processing of the retransmitting part16. As shown in FIG. 5, when detecting that the wireless LAN interface13 has failed in the transmission of a packet with respect to adestination wireless terminal and received a retransmission request, theretransmitting part 16 starts retransmission processing (Op 1). Theretransmitting part 16 initializes a variable r representing the currentnumber of transmissions (Op 2). After that, the retransmitting part 16determines whether or not the number of retransmissions has reached anupper limit (Op 3). Specifically, the retransmitting part 16 determineswhether or not the variable r representing the current number ofretransmissions is smaller than a variable r_max representing an upperlimit. FIG. 4B is a diagram showing examples of data on the variables rand r_max. Herein, r_max records the same value as the upper limit (seeFIG. 4A) of the number of retransmissions recorded by the retransmissionadjusting part 15.

The retransmitting part 16 initializes the variable r to be “0” at apredetermined period in parallel with the processing shown in FIG. 5.Consequently, the number of packet retransmissions is controlled at apredetermined period. Furthermore, the variable r_max is updated at apredetermined time interval by the retransmission adjusting part 15. Thepurpose for this is to update the upper limit value r_max in accordancewith the change in use situation of a bandwidth in the AP 1 a.

More specifically, the retransmitting part 16 compares the upper limitof the number of retransmissions to be updated in accordance with thebandwidth in use at a predetermined interval by the retransmissionadjusting part 15 with the current number of retransmissions.

In the case where the number of retransmissions has reached the upperlimit (No in Op 3), the retransmission processing is completed. In thecase where the number of retransmissions has not reached the upper limit(Yes in Op 3), the retransmitting part 16 transmits a packet whosetransmission has ended in failure to a destination wireless terminal viathe wireless LAN interface 13 (Op 4). In the case where the packettransmitted in Op 4 has reached the destination wireless terminal, morespecifically, the packet transmission has ended in success (Yes in Op5), the retransmission processing is completed.

In the case where the packet transmission has ended in failure (No in Op5), the retransmitting part 16 adds “1” to the variable r representingthe current number of retransmissions (Op 6), returns to Op 3 again, anddetermines whether or not the number of retransmissions has reached theupper limit. After that, the processes after Op 3 are repeated.Consequently, the packet retransmission is repeated until the number ofretransmissions reaches the upper limit.

(Operation Example 2 of Retransmission Adjusting Part 15 andRetransmitting Part 16)

A modified example of the operation will be described in which theretransmission adjusting part 15 determines an upper limit value of thenumber of packet retransmissions, and the retransmitting part 16retransmits a packet based on the upper limit value. FIG. 6A is adiagram showing data on an upper limit value of the number ofretransmissions in the modified example. As shown in FIG. 6A, theretransmission adjusting part 15 records an upper limit of the number ofretransmissions of each packet and an upper limit of the sum of thenumber of retransmissions within a constant length of time. The upperlimit of the number of retransmissions of each packet is calculated, forexample, in the same way as in the above-mentioned Operation example 1.The upper limit of the sum of the number of retransmissions within aconstant length of time can be determined based on a value obtained bydividing an entire available bandwidth in the AP 1 a by an averagebandwidth in use per communication.

An example of calculating an upper limit of the sum of the number ofretransmissions within a constant length of time using the data in thebandwidth management table 21 shown in FIG. 3 will be described below.It is understood from the data in the bandwidth management table 21 thatthe entire available bandwidth is “744 kbps”, and the average bandwidthin use per communication is “128 kbps”. The retransmission adjustingpart 15 can calculate “6” obtained by dividing “744 kbps” by “128 kbps”,followed by rounding off fractions of a decimal point of the obtainednumber as an upper limit of the sum of the number of retransmissionswithin a constant length of time.

FIG. 7 is a flowchart showing an example of the processing in which theretransmitting part 16 retransmits a packet, using an upper limit of thenumber of retransmissions of each packet and an upper limit of the sumof the number of retransmissions within a constant length of time. Inthe example shown in FIG. 7, the same operations as those in FIG. 5 aredenoted with the same reference numerals as those therein, and thedescription thereof will be omitted. After determining whether or notthe number of retransmissions of the packet to be retransmittedcurrently has reached the upper limit, the retransmitting part 16determines whether or not the sum of the number of retransmissionswithin a constant length of time has reached the upper limit (Op 3 a).The retransmitting part 16 makes the above determination based onwhether or not the variable R representing the sum of the number ofretransmissions within a constant length of time is smaller than thevariable R_max representing the upper limit. FIG. 6B shows examples ofdata on the variables r, r_max, R, and R_max. In r_max and R_max, thesame values as those of the upper limit (see FIG. 6A) of the number ofretransmissions recorded by the retransmission adjusting part 15 arerecorded. The retransmitting part 16 periodically initializes thevariable R to “0” at a period of the above-mentioned constant length oftime in parallel to the processing shown in FIG. 7. Consequently, thevariable R becomes a value representing the sum of the number of packetretransmissions within the constant length of time.

In the case where the sum of the number of retransmissions within aconstant length of time has reached the upper limit (No in Op 3 a), theretransmission processing is completed. Consequently, even if the numberof packet retransmissions has not reached the upper limit of the numberof retransmissions of each packet, when the sum of the number of packetretransmissions within a constant length of time has reached the upperlimit, the retransmitting part 16 does not perform a retransmission anymore. This can prevent the communication within a constant length oftime from being occupied with the retransmission processing to cause theshortage of a bandwidth. Furthermore, by setting the upper limit to thenumber of packet retransmissions within a constant length of time, evenif the upper limit of the number of retransmissions of each packet isset to be larger, the bandwidth can be prevented from being used up onlyby the retransmissions.

In the case where the sum of the number of retransmissions in apredetermined time has not reached the upper limit (Yes in Op 3 a), theretransmitting part 16 transmits a packet whose transmission has endedin failure (Op 4). In the case where the transmission of a packet hasended in success (Yes in Op 5), the retransmission processing iscompleted. In the case where the packet transmission has ended infailure (No in Op 5), the retransmitting part 16 adds “1” to thevariable r representing the current number of retransmissions, and alsoadds “1” to the variable R representing the sum of the number ofretransmissions (Op 6 a), whereby the processes after Op 3 are repeated.Consequently, until either the number of retransmissions of a packet tobe retransmitted or the sum of the number of retransmissions within aconstant length of time has reached an upper limit, the packetretransmission is repeated. It is preferable that the retransmissionadjusting part 15 updates the variable R_max at a predetermined timeinterval in accordance with the use situation of a bandwidth.Consequently, the upper limit value R_max is updated in accordance withthe change in the use situation of the bandwidth in the AP 1 a.

(Operation Example 3 of Retransmission Adjusting Part 15 andRetransmitting Part 16)

Next, another modified example of the operation will be described inwhich the retransmission adjusting part 15 determines an upper limitvalue of the number of packet retransmissions, and the retransmittingpart 16 retransmits a packet based on the upper limit value. FIG. 8A isa diagram showing data on an upper limit value of the number ofretransmissions in the present modified example. In the examples shownin FIG. 8A, an upper limit corresponding to each communicationidentifier representing the communication performed via the AP 1 a isrecorded. Furthermore, an upper limit of the number of retransmissionsof communication (other) other than the communication represented by thecommunication identifier and an upper limit of the sum of the number ofretransmissions within a constant length of time are recorded.

The retransmission adjusting part 15 can calculate an upper limit of thenumber of retransmissions for each communication, using a link speed, apriority, and an RSSI, as described in the above-mentioned Operationexample 1. Thus, by setting an upper limit value for each communication,the quality of communication can be adjusted for each communication.

A method for calculating an upper limit of the number of retransmissionsfor each communication is not limited to the method described in theabove Operation example 1. For example, in the case of relaying a packetof multi-medium communication including a stream of a plurality ofmedium types such as a voice stream and a video stream through the AP 1a, the retransmission adjusting part 15 can also change an upper limitvalue of the number of retransmissions depending upon the media type ofa stream, for example. Consequently, the retransmission control suitablefor a medium type of each stream can be performed. In this case, theretransmission adjusting part 15 can assign weights in accordance witheach medium type to the upper limit of the number of retransmissions foreach medium type. For example, the retransmission adjusting part 15 canset, as an upper limit of the number of retransmissions in each stream,a value obtained by multiplying the upper limit of the number ofretransmissions recorded in the retransmission number recording part 18by 1.5 regarding a voice stream, and can set, as an upper limit of thenumber of retransmissions in each stream, a value obtained bymultiplying the upper limit of the number of retransmissions by 0.7regarding a video stream.

Examples of a method for identifying a medium type such as a voicestream and a video stream included in multi-medium communication includea method for obtaining information regarding a medium type included in apacket. Specifically, the bandwidth management part 14 can obtain amedium type included in a stream with reference to the SDP data of theinvite packet.

FIG. 9 is a flowchart showing an example of the processing ofretransmitting a packet, using an upper limit of the number ofretransmissions of each packet for each communication and an upper limitof the sum of the number of retransmissions within a constant length oftime. In the example shown in FIG. 9, the same operations as those inFIG. 7 are denoted with the same reference numerals as those therein,and the description thereof will be omitted. When startingretransmission processing, the retransmitting part 16 obtains acommunication identifier from a packet whose transmission has ended infailure (Op 1 a). The communication identifier can be, for example, anIP address and a port number of a wireless terminal that performscommunication. In Op 3, when determining whether or not the number ofretransmissions has reached an upper limit, the retransmitting part 16uses values corresponding to the communication represented by thecommunication identifier obtained in the OP 1 a as the variable rrepresenting the current number of retransmissions and the variabler_max representing the upper limit.

FIG. 8B is a diagram showing examples of data on the variables r andr_max corresponding to the respective communication identifiers. Forexample, in the case where the communication identifier obtained by theretransmitting part 16 in the Op 1 a is “192.168.0.100:32267”, in thedata shown in FIG. 8B, the upper limit value “3” is used as r_max, withthe current number “1” of retransmissions corresponding to the databeing r. Consequently, the retransmitting part 16 can retransmit apacket by varying the upper limit of the number of retransmissions inaccordance with the communication identifier of a packet to beretransmitted.

Although the operation example of the retransmission adjusting part 15and the retransmitting part 6 has been described, the operations of theretransmission adjusting part 15 and the retransmitting part 16 are notlimited to the above example.

Embodiment 2

In the present embodiment, the function of controlling a packetretransmission at a wireless terminal is added to Embodiment 1, FIG. 10is a functional block diagram showing a configuration of the AP 10 aaccording to the present embodiment. In FIG. 10, the same functionalblocks as those in FIG. 2 are denoted with the same reference numeralsas those therein, and the description thereof will be omitted. The AP 10a shown in FIG. 10 further includes a beacon generating part 23.Furthermore, the wireless terminal 30 a includes a wireless LANinterface 24, a beacon analyzing part 25, a retransmission numbersetting part 26, a retransmission number recording part 18 a, and aretransmitting part 16 a. a wireless terminal 30 b can also have asimilar configuration.

The beacon generating part 23 of the AP 10 a notifies the wirelessterminals 30 a, 30 b of the upper limit of the number of retransmissionsdetermined by the retransmission adjusting part 15, using a beacon. Thebeacon generating part 23 generates a beacon including an upper limit ofthe number of retransmissions determined by the retransmission adjustingpart 15, and transmits the beacon to the wireless terminals 30 a and 30b via the wireless LAN interface 13. The beacon generating part 23 canrecord an upper limit of the number of retransmissions, for example, ina bender-specific portion of the beacon.

The retransmission adjusting part 15 updates an upper limit of thenumber of retransmissions on a predetermined time basis. Therefore, thebeacon generating part 23 can also transmit a beacon including anupdated upper limit of the number of retransmissions on a predeterminedtime basis in accordance with the timing of the update. The timing fornotification of the upper limit of the number of retransmissions is notlimited thereto. The beacon generating part 23 may make a notificationof an upper limit of the number of retransmissions at the start ofcommunication or for each packet transmission.

In the case of making a notification of the number of retransmissionsvarying depending upon the plurality of terminals, the beacon generatingpart 23 sends a beacon containing a combined data on a terminal ID foridentifying a wireless terminal and an upper limit of the number ofretransmissions.

At the wireless terminal 30 a, the wireless LAN interface 24 receivesthe beacon sent from the beacon generating part 23 and passes the beaconto the beacon analyzing part 25. The beacon analyzing part 25 analyzesthe given beacon, obtains data representing the upper limit of thenumber of retransmissions, and passes the data to the retransmissionnumber setting part 26. The retransmission number setting part 26records the upper limit of the number of retransmissions in theretransmission number recording part 18 a. The retransmission numberrecording part 18 a can record data with the same configuration as thatrecorded in the retransmission number recording part 18 of the AP 10 a.The retransmitting part 16 a performs the retransmission processing of apacket in accordance with the upper limit of the number ofretransmissions recorded in the retransmission number recording part 18a. The function of the retransmitting part 16 a is the same as that ofthe retransmitting part 16 of the AP 10 a.

Consequently, the wireless terminal 30 a can retransmit a packet basedon the upper limit of the number of retransmissions determined in the AP10 a. Therefore, a retransmission can be performed in accordance withthe bandwidth use situation in the entire radio communication by the AP10 a.

In the present embodiment, an example has been shown in which a wirelessterminal is notified of the upper limit of the number of retransmissionsusing a beacon. However, the method for notifying a wireless terminal ofthe upper limit of the number of retransmissions is not limited thereto.For example, a wireless terminal can also be notified of the upper limitof the number of retransmissions, using a packet of an application layersuch as an ack packet of the SIP. In the case of notifying a wirelessterminal of the upper limit of the number of retransmissions for eachpacket to be sent to the wireless terminal, it is advantageous in termsof the saving of a bandwidth in use, to use an ack packet.

Embodiment 3

FIG. 11 is a functional block diagram showing a configuration of an AP100 a according to the present embodiment. In FIG. 11, the samefunctional blocks as those in FIG. 2 are denoted with the same referencenumerals as those therein, and the description thereof will be omitted.An AP 100 a shown in FIG. 11 further includes a retransmission historyrecording part 31. The retransmitting part 16 a has a function that isnot present in the retransmitting part 16 shown in FIG. 2. Theretransmitting part 16 a determines a transmission interval at which apacket is retransmitted with reference to the retransmission historyrecording part 31, and retransmits a packet at the determinedtransmission interval. The retransmission history recording part 31records a retransmission timing of a packet and a packet transmissionsuccess rate at that retransmission timing in such a manner that theyare associated with each other. It is preferable that, every time theretransmitting part 16 a retransmits a packet, it updates the datarecorded in the retransmission history recording part 31.

FIG. 12 is a diagram showing examples of data to be recorded in theretransmission history recording part 31. In a retransmission historytable 32 shown in FIG. 12, a terminal ID, a retransmission timing, and apacket transmission success rate are recorded in such a manner that theyare associated with each other. The terminal ID is an identifier of awireless terminal to be a packet destination. For example, a MACaddress, an IP address, other nicknames, or the like can be used as aterminal ID. In the retransmission history table 32, as a retransmissiontiming, identifiers (“0”, “1”, “2”, “3”, “4”, “5”) for identifying aperiod from a time when the retransmission history table 32 receives aretransmission request to a time when it retransmits a packet arerecorded.

Specific examples of a time associated with each identifier include aproportion pattern to be (Time corresponding to identifier n)=n×ConstantT regarding an identifier n (n is an integer of 0 or more). In thisproportion pattern, for example, assuming that Constant T=50 (μseconds),an identifier “0” is associated with 0 (μseconds), “1” is associatedwith 50 (μseconds), “2” is associated with 100 (μseconds), “3” isassociated with 150 (μseconds), “4” is associated with 200 (μseconds),and “5” is associated with 250 (μseconds). Furthermore, as anotherpattern, there is the pattern of a power in which (Time corresponding toidentifier n)=(Time corresponding to identifier n−1)×Constant T1 (Timecorresponding to n=0 is 0 (μseconds), Time corresponding to n=1 isConstant T2) in n>1. In this pattern of a power, for example, assumingthat Constant T1=2 and Constant T2=50 (μseconds), the time of anidentifier “0” is associated with 0 (μseconds), “1” is associated with50 (μseconds), “2” is associated with 100 (μseconds), “3” is associatedwith 200 (μseconds), “4” is associated with 400 (μseconds), and “5” isassociated with 800 (μseconds).

The packet transmission success rate is represented, for example, by aprobability (%) at which the transmission of a retransmitted packet hasended in success. In FIG. 12, a part of the description recorded in theretransmission history table 32 is omitted. Furthermore, the data to berecorded in the retransmission history recording part 31 is not limitedto the retransmission history table 32 shown in FIG. 12. For example,data representing a relationship between a retransmission timing and apacket transmission success rate may be recorded, for example, for eachcommunication identifier or available bandwidth, instead of a terminalID.

FIG. 13 is a flowchart showing an operation example of theretransmitting part 16 a. In FIG. 13, the same operations as those inFIG. 7 are denoted with the same reference numerals as those therein,and the description thereof will be omitted. When startingretransmission processing, the retransmitting part 16 a obtains aterminal ID from a packet whose transmission has ended in failure (Op 1b). The retransmitting part 16 a determines a retransmission timing,with reference to a retransmission timing and a packet transmissionsuccess rate corresponding to the obtained terminal ID in theretransmission history table 32 (Op 1 c). The retransmitting part 16 aselects, for example, a retransmission timing at which the success rateis highest among the retransmission timings recorded in theretransmission history table 32. In the example shown in FIG. 12, “5” isselected. Then, the retransmitting part 16 a generates a random numberat which the probability of the selected retransmission timing becomeshighest, and determines a retransmission timing in accordance with therandom number. For example, the retransmitting part 16 a generateseither of “0” to “5” in a random order so that the occurrenceprobability of the selected retransmission timing “5” is 50%, and eachoccurrence probability of “0” to “4” is 10%. The generated number is setto be a retransmission timing. Consequently, the transmission successrate of each retransmission timing can be obtained. The method fordetermining a retransmission timing is not limited thereto. Theretransmitting part 16 a may set the selected retransmission timing tobe a retransmission timing as it is, for example. In the case ofretransmitting the same packet a plurality of times, the number oftransmissions at the selected retransmission timing may be set to belargest.

When the retransmission timing is determined, the retransmitting part 16a determines whether or not the number of packet retransmissions and thesum of the number of retransmissions within a constant length of timehas reached an upper limit (Op 3, Op 3 a). In the case of Yes in Op 3and Op 3 a, after standing by in accordance with the retransmissiontiming determined in Op 1 c (Op 4 c), the retransmitting part 16 a sendsa packet (Op 4). The processes after the packet transmission (Op 4) arethe same as those in FIG. 7. Due to the stand-by in Op 4 a, a packet canbe sent at a timing at which the possibility of success of packettransmission is high. In general, even if a packet is retransmittedimmediately after the transmission thereof has ended in failure, theretransmission is unlikely to succeed since communication conditions donot change in most cases. Therefore, the retransmitting part 16 a canenhance the success rate of the packet transmission by delaying aretransmission timing. Furthermore, during the stand-by in Op 4 a, thebandwidth becomes excess accordingly. Therefore, the bandwidth can beeffectively utilized by sending another packet through the wireless LANinterface 13.

Embodiment 4

FIG. 14 is a functional block diagram showing a configuration of an AP101 a according to the present embodiment. In FIG. 14, the samefunctional blocks as those in FIG. 2 are denoted with the same referencenumerals as those therein. The AP 101 a further includes a transmissionhistory recording part 33 and an information collecting part 34.Furthermore, a retransmitting part 16 b has a function that is notpresent in the retransmitting part 16 shown in FIG. 2. The informationcollecting part 34 records a link speed and a packet transmissionsuccess rate of a packet sent by the wireless LAN interface 13 towireless terminals 3 a, 3 b in a communication area in the transmissionhistory recording part 33. The transmitting part 16 b selects a linkspeed at which a packet transmission success rate is expected toincrease, with reference to data recorded in the transmission historyrecording part 33, and retransmits a packet at a link speed based on theselected link speed. The retransmitting part 16 b may apply a link speedso that the probability at which a packet is transmitted at the selectedlink speed becomes highest in the same way as in the case of aretransmission timing in Embodiment 3. Consequently, a packet can besent at various link speeds, and a transmission success rate withrespect to various link speeds can be obtained.

FIG. 15 is a diagram showing examples of data recorded in thetransmission history recording part 33. In the example shown in FIG. 15,the link speed of a packet sent by the wireless LAN interface 13 and thedata representing a history of a packet transmission success rate arerecorded in three link speed history tables 35 a, 35 b, and 35 c. Thelink speed history table 35 a stores a history during a peak time(available bandwidth: 100 kbps or less). The link speed history table 35b stores a history during an intermediate time (available bandwidth: 101kbps to 300 kbps). The link speed history table 35 c stores a historyduring an off-peak time (available bandwidth: 301 kbps or more). In eachof the link speed history tables 35 a, 35 b, and 35 c, a plurality ofsets of data in which a link speed and a packet transmission successrate at the link speed are one set are recorded for each communicationidentifier.

The information collecting part 34 obtains a link speed of a packet tobe sent by the wireless LAN interface 13 to a destination wirelessterminal, and information representing whether or not the sent packethas reached the destination wireless terminal (success/failure intransmission), and records them in a temporary recording region such asa memory. Furthermore, the information collecting part 34 simultaneouslyobtains an available bandwidth during each packet transmission from thebandwidth information recording part 17, and records the availablebandwidth in the temporary recording region so that the availablebandwidth is associated with a link speed for each packet andinformation representing the success/failure in transmission. Then,regarding a peak time, an intermediate time, and an off-peak time, theinformation collecting part 34 summarizes a packet transmission successrate for each link speed at a constant time interval. Thus, in the linkspeed history tables 35 a, 35 b, and 35 c, a link speed and a packettransmission success rate of packet transmission by the wireless LANinterface 13 at a constant time interval are reflected at all times.

The retransmitting part 16 b determines a link speed for retransmittinga packet whose transmission has ended in failure with reference to thelink speed history tables 35 a, 35 b, or 35 c. FIG. 16 is a flowchartshowing an operation example of the retransmitting part 16 b. In FIG.16, the same operations as those in FIG. 7 are denoted with the samereference numerals as those therein, and the description thereof will beomitted. When starting retransmission processing, the retransmittingpart 16 b obtains a communication identifier from the packet whosetransmission has ended in failure (Op 1 d). Furthermore, theretransmitting part 16 b obtains an available bandwidth from thebandwidth information recording part 17 (Op 1 e). After that, theretransmitting part 16 b applies a link speed with reference to the datarecorded in the transmission history recording part 33 based on thecommunication identifier and the available bandwidth (Op 1 f).

As an example, the case will be described in which, when thecommunication identifier obtained in Op 1 d is “192.168.0.100:32267” andthe available bandwidth is “75 kbps”, the retransmitting part 16 bapplies a link speed with reference to the data shown in FIG. 15. Inthis case, since the available bandwidth is “75 kbps” which is lowerthan 100 kbps, so that the retransmitting part 16 b refers to the linkspeed history table 35 a during a peak time. Then, the retransmittingpart 16 b selects a link speed “5.5 Mbps” at which a packet transmissionsuccess rate is highest among the link speeds of the communicationidentifier “192.168.0.100:32267” of the link speed history table 35 a.The retransmitting part 16 b determines a link speed during packetretransmission based on the selected link speed “5.5 Mbps”.Consequently, a link speed suitable for a peak time of the communicationrepresented by the communication identifier “192.168.0.100:32267” isobtained.

When the link speed is applied, the retransmitting part 16 b determineswhether or not the number of packet retransmissions and the sum of thenumber of retransmissions within a constant length of time has reachedan upper limit (Op 3, Op 3 a). In the case of Yes in Op 3 and Op 3 a,the retransmitting part 16 b sends a packet at the link speed applied inOp 1 f (Op 4). Consequently, the retransmitting part 16 b can send apacket at a link speed in accordance with the available bandwidth. Theprocesses in Op 4 and subsequent operations are the same as those inFIG. 7.

The data to be recorded in the link speed history recording part is notlimited to the examples shown in FIG. 15. For example, as shown in FIG.15, values representing a link speed and a packet transmission successrate may be recorded for each communication identifier in one table,without a table being divided in accordance with the availablebandwidth. Furthermore, only a packet transmission success rate may berecorded for each communication identifier. In this case, theretransmitting part 16 b can apply a link speed based on a packettransmission success rate. For example, the retransmitting part 16 bretransmits a packet with a link speed decreased in the case where thepacket transmission success rate is less than a predetermined thresholdvalue, whereby the possibility for a retransmission packet to reach adestination wireless terminal can be enhanced. Thus, the data to berecorded in the link speed history recording part only need to representa relationship between a link speed and a packet transmission successrate.

Embodiment 5

FIG. 17 is a functional block diagram showing a configuration of the AP102 a according to the present embodiment. In FIG. 17, the samefunctional blocks as those in FIG. 2 are denoted with the same referencenumerals as those therein, and the description thereof will be omitted.The AP 102 a further includes a packet loss history recording part 36and an acceptable information recording part 37. Furthermore, aretransmitting part lGc and a packet monitoring part 12 c have functionsthat are not present in the retransmitting part 16 and the packetmonitoring part 12 shown in FIG. 2.

The packet loss history recording part 36 records a history of a packetloss caused by the packet transmission failure of the wireless LANinterface 13 with respect to the respective wireless terminals 3 a, 3 b.The data of the packet loss history recording part 36 is updated alwaysin accordance with the packet transmission situation of the wireless LANinterface 13. FIG. 18 shows examples of data to be recorded in thepacket loss history recording part 36. In the packet loss history table38 shown in FIG. 18, the count of sequential packet losses is recordedfor each terminal ID. For example, the packet transmission of a terminalID=“terminal A” with respect to a wireless terminal has ended infailure, and the retransmitting part 16 c has not succeeded in packettransmission even when it repeats packet retransmission until the numberof retransmissions reaches an upper limit, the packet is discarded. Morespecifically, a packet loss occurs. At this time, an update of adding 1to the count of sequential packet losses of the terminal A of the packetloss history table 38 is performed. After that, when the packettransmission to the terminal A ends in success, the count of sequentialpacket losses is reset to “0”. Conversely, when packet losses occurcontinuously, the count of sequential packet losses is incremented.Consequently, the count of sequential packet losses is recorded in thepacket loss history table 38.

The packet monitoring part 12 c obtains data that represents thecondition of the count of sequential packet losses acceptable in radiocommunication of the wireless terminals 3 a and 3 b from the packetreceived by the wireless LAN interface 13 and records it in theacceptable information recording part 37. For example, in the case wherethe wireless terminals 3 a, 3 b can use a PLC (packet loss concealment)technique, the wireless terminals 3 a, 3 b send a PLC information packetfor making a notification of PLC information to the AP 102 a. The PLCinformation packet contains data representing the condition of the countof sequential packet losses acceptable in a communication. Whendetecting the PLC information packet, the packet monitoring part 12 crecords the contents thereof in the acceptable information recordingpart 37. Thus, in the acceptable information recording part 37, datarepresenting the condition of the count of sequential packet lossesacceptable in radio communication by the wireless terminals 3 a, 3 b arerecorded.

FIG. 19 shows examples of data to be recorded in the acceptableinformation recording part 37. In the examples shown in FIG. 19, anupper limit and a lower limit of a range of a count of sequential packetlosses that cannot be accepted are recorded for each terminal ID. Forexample, in the case where the count of sequential packet losses is notin a range of the lower limit “2” to the upper limit “5”, the data of aterminal ID=“terminal A” shows that a packet loss is acceptable. Thereason for this is as follows: when the count of sequential packetlosses is the lower limit “2” or less, it is not necessary to retransmita packet since the degradation in sound quality caused by a packet losscan be concealed by the PLC technique, and when the packet loss is theupper limit “5” or more, the degradation in sound quality has alreadybeen remarkable, so that it is not necessary to send a packet even byretransmitting it. The values of the lower limit and the upper limit aredetermined depending upon the ability of the PLC function of a terminal.

The retransmitting part 16 c obtains the count of sequential packetlosses at the destination wireless terminal (for example, referred to asthe wireless terminal 3 a) of a packet to be retransmitted from thepacket loss history recording part 36. Furthermore, the retransmittingpart 16 c determines whether or not the obtained count of sequentialpacket losses corresponds to the condition of the count of sequentialpacket losses acceptable in radio communication of the wireless terminal3 a, with reference to the acceptable information recording part 37, anddiscards the packet without retransmitting it in the case where thecount corresponds to the condition.

FIG. 20 is a flowchart showing an operation example of theretransmitting part 16 c. In FIG. 20, the same operations as those inFIG. 7 are denoted with the same reference numerals as those therein,and the description thereof will be omitted. When startingretransmission processing, the retransmitting part 16 c obtains aterminal ID of a packet whose transmission has ended in failure (Op 1g). Furthermore, the retransmitting part 16 c obtains the count ofsequential packet losses of a wireless terminal represented by theterminal ID from the packet loss history recording part 36 (Op 1 h). Forexample, in the case where Terminal ID=“Terminal A”, the retransmittingpart 16 c obtains a count of sequential packet losses “0” from thepacket loss history table 38 shown in FIG. 18.

Furthermore, the retransmitting part 16 c obtains acceptable conditionsof a count of sequential packet losses of a wireless terminalrepresented by a terminal ID from the acceptable information recordingpart 37 (Op 1 i). For example, in the case where terminal ID=“TerminalA”, the retransmitting part 16 c obtains the lower limit “3” and theupper limit “5,” of the count of sequential packet losses for whichpacket losses cannot be accepted from the data shown in FIG. 19.

Next, the retransmitting part 16 c determines whether or not the countof sequential packet losses obtained in Op 1 h satisfies the acceptableconditions obtained in Op 1 i (Op 1 j). For example, in the case whereTerminal ID=“Terminal A”, the count of sequential packet losses “0” isnot in a range of the lower limit “3” to the upper limit “5” of thecount of sequential packet losses for which packet losses cannot beaccepted, so that the retransmitting part 16 c determines that thepacket loss acceptable conditions are satisfied. In this case, theprocessing is completed without sending a packet.

For example, in the case where the count of sequential packet lossesobtained in Op 1 h is “3”, etc, the packet loss acceptable conditionsare not satisfied. Therefore, the retransmitting part 16 c performs theprocesses in Op 2 and subsequent processes. The processes in Op 2 andsubsequent processes are the same as those in FIG. 7. More specifically,in the case where the count of sequential packet losses is in a range of“3”, to “5”, a packet is retransmitted. The upper limit of theretransmission number in this case is an upper limit of theretransmission number determined by the retransmission adjusting part15.

As described above, due to the processing shown in FIG. 20, in the casewhere a packet loss is acceptable at a wireless terminal of a packetdestination, the retransmitting part 16 c does not need to retransmit apacket. Consequently, the increase in a bandwidth in use by theretransmission of a packet can be suppressed.

The present embodiment can be applied to special communication, forexample, among communications with sequence numbers allocated topackets. More specifically, the present embodiment can be applied to thefollowing communication: even if packets of partial sequence numbersdrop out, there is no effect on the communication quality; however, whensequence numbers drop out sequentially, the communication quality isdegraded. Examples of such communication include voice communication andvideo communication.

In order to keep the above-mentioned communication in high quality,sequence numbers may be prevented from dropping out sequentially.Therefore, as shown in FIG. 18 in the present embodiment, the count ofsequential packet losses is stored for each communication.

Then, as shown in FIG. 19, in the case where the count of sequentialpacket losses is small to such a degree that the quality is notdegraded, the upper limit of the packet retransmission number is set tobe a small number of times (or 0). This saves a bandwidth. In the casewhere the count of sequential packet losses is large to such a degreethat the quality is degraded remarkably, the upper limit of the packetretransmission number is set to be a large number of times. This keepsthe quality. Furthermore, in the case where the count of sequentialpacket losses is an extremely large number of times, the upper limit ofthe packet retransmission number is set to be a small number of times(or 0), whereby the bandwidth can be saved. This is because, in the casewhere the count of sequential packet losses is an extremely large numberof times, the rapid improvement of a situation cannot be expected.

Thus, according to the present embodiment, the quality of theabove-mentioned communication can be kept high while the bandwidth isbeing saved.

Embodiment 6

FIG. 21 is a functional block diagram showing a configuration of an AP103 a according to the present embodiment. In FIG. 21, the samefunctional blocks as those in FIG. 2 are denoted with the same referencenumerals as those therein, and the description thereof will be omitted.The AP 103 a shown in FIG. 21 further includes a priority control part38. Furthermore, in the bandwidth information recording part 17, aprioritized communication identifier representing prioritizedcommunication of relaying a packet by priority is recorded. Morespecifically, the bandwidth managing part 14 records only information onthe communication of a packet to be relayed by priority in the bandwidthinformation recording part 17.

The priority control part 38 controls the wireless LAN interface 13 soas to relay a packet (hereinafter, referred to as a prioritized packet)of communication recorded in the bandwidth information recording part 17by priority. As a system for relaying a packet by priority, for example,a prioritized communication system in conformity with IEEE 802.11e canbe used. For example, in the case where the transmission of aprioritized packet and the transmission of a non-prioritized packetoccur simultaneously, the priority control part 38 can control thewireless LAN interface 13 so as to send the prioritized packet inadvance.

Even in the present embodiment, in the bandwidth information recordingpart 17, for example, data shown in FIG. 3 is recorded. A packet ofcommunication represented by a communication identifier recorded in thebandwidth management table 21 shown in FIG. 3 is relayed by priority.More specifically, the communication represented by the communicationidentifier recorded in the bandwidth management table 21 is prioritizedcommunication. As an example of the prioritized communication, real-timecommunication such as telephone communication is assumed. Furthermore,as an example of the non-prioritized communication that is not recordedin the bandwidth management table 21, data communication such as HyperText Transfer Protocol (HTTP) and File Transfer Protocol (FTP) isassumed.

FIG. 22A is a diagram showing data to be recorded in the retransmissionnumber recording part 18 in the present embodiment. In the example shownin FIG. 22A, upper limits respectively corresponding to communicationidentifiers representing communication performed via the AP 103 a arerecorded. Furthermore, an upper limit of the retransmission number ofcommunication (Other: non-prioritized communication) other than thecommunication represented by the communication identifier, and an upperlimit of the sum of the number of retransmissions within a constantlength of time are recorded. Herein, the upper limit “10” that is thenumber of retransmissions of non-prioritized communication is apreviously fixed value, and is not updated by the retransmissionadjusting part 15. The upper limit other than the upper limit of thenumber of retransmissions of non-prioritized communication is updatedfor each constant time by the retransmission adjusting part 15 in thesame way as in Embodiment 1.

In the case where the transmission of a prioritized packet and thetransmission of a non-prioritized packet occur simultaneously, when aprioritized packet is set to be sent in advance without fail, the effectof reducing a data loss in non-prioritized communication is obtained bysetting the upper limit of the number of retransmissions of anon-prioritized packet to be a relatively high fixed value. As anexample of the non-prioritized communication, data communication such asHTTP and FTP is assumed. In such data communication, unlike thereal-time communication such as telephone conversation assumed to beprioritized communication, although the delay of a packet is acceptable,the loss of a packet is not acceptable. For example, a compressed fileto be sent in data communication cannot be decompressed if there is anerror of 1 bit. Therefore, in the case where a data loss occurs, a losspacket is retransmitted often by an application through which the packethas been sent. In this case, communication is performed again over theentire communication path, so that excess traffic increases in thecommunication path and excess processing is performed even in theapplication. Therefore, in data communication, it is more efficient todecrease a data loss by accepting a largest possible number ofretransmissions at the AP 103 a and the wireless terminals 3 a, 3 b.

For example, in the case where the transmission of a prioritized packetand the transmission of a non-prioritized packet occur simultaneously,when a prioritized packet is set to be sent in advance at apredetermined probability of less than 100%, there is a possibility thatthe retransmission of a packet in the non-prioritized communication mayimpose strain on the communication bandwidth of prioritizedcommunication. In this case, the retransmission adjusting part 15 maychange the upper limit of the number of retransmissions of thenon-prioritized communication in accordance with a bandwidth in usewithout setting the upper limit of the number of retransmissions in thenon-prioritized communication to be a fixed value.

FIG. 23 is a flowchart showing an example of the processing in which theretransmitting part 16 d retransmits a packet. In the example shown inFIG. 23, the same operations as those in FIG. 5 are denoted with thesame reference numerals as those therein, and the description thereofwill be omitted. When starting retransmission processing (Op 1), theretransmitting part 16 d obtains a communication identifier from apacket whose transmission has ended in failure (Op 1 a).

In the processing in which the retransmitting part 16 d determineswhether or not the number of retransmissions has reached an upper limitin Op 3, an upper limit value r_max varies depending upon thecommunication identifier obtained in Op 1 a. An example thereof will bedescribed below. FIG. 22B is a prioritized communication diagram showingexamples of data on variables r and r_max used in the determination inOp 3. The values r_max shown in FIG. 22B are the same as the upper limitvalues shown in FIG. 22(B). More specifically, with respect to a packethaving a communication identifier in prioritized communication, an upperlimit determined by the retransmission adjusting part 15 for eachcommunication identifier is used for the value of r_max, and withrespect to a packet having a communication identifier of non-prioritizedcommunication, a fixed value “10” is used as the value of r_max. Becauseof this, the upper limit of the number retransmissions of a packet inprioritized communication is an upper limit to be updated in accordancewith the use situation of a bandwidth, and the upper limit of the numberof retransmissions of a packet in non-prioritized communication is apreviously determined fixed upper limit.

Furthermore, the retransmitting part 16 d determines whether or not apacket whose transmission has ended in failure is a packet inprioritized communication or a packet in non-prioritized communication,with reference to the retransmission number recording part 18, based onthe obtained communication identifier (Op 4 b). For example, in the casewhere the obtained communication identifier is “192.168.0.100:32267”,the retransmitting part 16 d can determine that the communication of thepacket whose transmission has ended in failure is prioritizedcommunication, since the communication identifier is recorded, withreference to the data shown in FIG. 22A.

If the packet whose transmission has ended in failure is a packet inprioritized communication (Yes in Op 4 d), the packet is sent bypriority through the wireless LAN interface 13 (Op 4 c). If the packetwhose transmission has ended in failure is not a packet in prioritizedcommunication (No in Op 4 b), the packet is sent by non-prioritizedthrough the wireless LAN interface 13 (Op 4 d). More specifically, aretransmission packet in prioritized communication is assigned abandwidth by priority. Therefore, in the case where a bandwidth isinsufficient in the radio communication of the AP 103 a, a packet inprioritized communication is sent by priority, so that the packet innon-prioritized communication is delayed.

As described above, due to the operation shown in FIG. 23, in the casewhere a bandwidth is insufficient, the upper limit of the number ofretransmissions is suppressed to prevent a delay in prioritizedcommunication, and a predetermined number of retransmissions is ensuredin non-prioritized communication, although the possibility of a delayincreases. Therefore, a packet loss is suppressed, and the possibilitythat packets can be sent in the order of a packet arrival increases. Forexample, by setting data communication in non-prioritized communication,with the real-time voice communication such as telephone conversationbeing prioritized communication, in the real-time voice communication,the delay of a packet can be suppressed, and in the data communication,a packet can be sent with reliability kept constantly in the order of apacket arrival.

As described above, in Embodiments 1-6, as an example, the configurationand operation of an AP for a wireless LAN has been described. Thewireless LAN is a specification of a short-distance wireless networkdetermined by IEEE 802.11. However, the relay apparatus according to thepresent invention is not limited to an AP for a wireless LAN. Forexample, the relay apparatus of the present invention is also applicableto an AP for a wireless metropolitan area network (MAN) that is aspecification of a long-distance wireless network determined by WiMAX.

Furthermore, in the above-mentioned embodiment, although the case hasbeen described in which the wireless terminals 3 a-3 d, 30 a, and 30 bare those which have a function of an IP telephone, the function of thewireless terminals is not limited to that of the IP telephone. Thewireless terminals may have functions of, for example, a videoreproducing terminal, a PDA, an electronic organizer, a game machine,and a GPS terminal. Furthermore, the communication of a wirelessterminal whose start is controlled by the SIP server 2 is not limited tovoice communication. Examples of the communication of the wirelessterminals include video distribution, music distribution, an onlinegame, stock price information distribution, remote presentation, a TVconference, and monitoring camera image transmission.

The present invention can be used as a relay apparatus for relayingcommunication by a plurality of wireless terminals in a communicationarea while keeping constant communication quality in a limitedbandwidth.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

1. A relay apparatus for relaying a packet to be transmitted in radiocommunication by at least one wireless terminal in a communication area,comprising: a packet monitoring part for obtaining data on a bandwidthused in the radio communication by the wireless terminal from the packetto be relayed by the relay apparatus; a bandwidth managing part forcalculating and recording a total bandwidth in use used for the radiocommunication by the wireless terminal in the communication area basedon the data obtained by the packet monitoring part; a retransmissionadjusting part for determining an upper limit of a packet retransmissionnumber in accordance with an amount of an available bandwidth obtainedby excluding the total bandwidth in use from a maximum bandwidthavailable in the radio communication by the wireless terminal; and aretransmitting part for retransmitting a packet whose transmission hasended in failure by the relay apparatus, in a range not exceeding theupper limit of the packet retransmission number determined by theretransmission adjusting part.
 2. The relay apparatus according to claim1, wherein the retransmission adjusting part divides the availablebandwidth by the number of wireless terminals that perform the radiocommunication in the communication area to obtain an available bandwidthper wireless terminal, and determines the upper limit of the packetretransmission number for each wireless terminal, using the availablebandwidth per wireless terminal.
 3. The relay apparatus according toclaim 1, wherein the retransmission adjusting part sets the upper limitof the packet retransmission number by the relay apparatus within aconstant length of time in accordance with the available bandwidth. 4.The relay apparatus according to claim 1, wherein the retransmissionadjusting part sets the upper limit of the packet retransmission numberfor each radio communication performed by the wireless terminal.
 5. Therelay apparatus according to claim 1, further comprising a transmissionhistory recording part for recording a communication identifier foridentifying communication of the packet to be relayed by the relayapparatus and relationship data that represents a relationship between alink speed in communication represented by the communication identifierand a packet transmission success rate, wherein when retransmitting thepacket of the communication represented by the communication identifierrecorded in the transmission history recording part, the retransmittingpart applies a link speed at which the packet transmission success ratein the communication represented by the communication identifier ishighest based on the relationship data, and retransmits the packet basedon the applied link speed.
 6. The relay apparatus according to claim 1,further comprising a retransmission history recording part for recordingrelationship data that represents a relationship between aretransmission timing of a packet retransmitted by the retransmittingpart and a packet transmission success rate, wherein the retransmittingpart determines a retransmission timing at which the packet transmissionsuccess rate is highest based on the relationship data, and determines atransmission interval at which a packet whose transmission has ended infailure by the relay apparatus based on the determined retransmissiontiming.
 7. The relay apparatus according to claim 1, further comprising:a packet loss history recording part for recording a history of a packetloss caused by a packet transmission failure of the relay apparatus foreach wireless terminal; and an acceptable information recording part forrecording data that represents a condition of a count of sequentialpacket losses acceptable in the radio communication for each wirelessterminal, wherein the packet monitoring part obtains data thatrepresents a condition of the count of sequential packet lossesacceptable in the radio communication of the wireless terminal from apacket to be relayed by the relay apparatus and records the data in theacceptable information recording part, and the retransmitting partobtains a count of sequential packet losses at a destination wirelessterminal of a packet to be retransmitted from the packet loss historyrecording part, determines whether or not the obtained count ofsequential packet losses corresponds to the condition of the count ofthe sequential packet losses acceptable in the radio communication ofthe destination wireless terminal represented by the data recorded inthe acceptable information recording part, and in a case where theobtained count of sequential packet losses corresponds to the condition,discards the packet without retransmitting it.
 8. The relay apparatusaccording to claim 1, further comprising a retransmission number sendingpart for notifying the wireless terminal of an upper limit of the packetretransmission number determined by the retransmission adjusting part.9. The relay apparatus according to claim 1, further comprising: apriority communication recording part for recording a prioritizedcommunication identifier that represents prioritized communicationthrough which the relay apparatus relays a packet by priority; and apriority control part for sending the packet in the prioritizedcommunication represented by the prioritized communication identifier bypriority, wherein the retransmission adjusting part determines an upperlimit of a packet retransmission number, in accordance with an amount ofan available bandwidth obtained by excluding the total bandwidth in usefrom the maximum bandwidth available in the radio communication of therelay apparatus, only with respect to a packet of the prioritizedcommunication, and the retransmitting part retransmits the packet in theprioritized communication represented by the prioritized communicationidentifier among packets whose transmissions have ended in failure bythe relay apparatus in a range not exceeding the upper limit of thepacket retransmission number determined by the retransmission adjustingpart, and retransmits a packet in communication other than theprioritized communication represented by the prioritized communicationidentifier among packets whose transmissions have ended in failure bythe relay apparatus by a predetermined number of times.
 10. A relaymethod for relaying a packet to be transmitted in radio communication byat least one wireless terminal in a communication area, comprising:obtaining data on a bandwidth used in the radio communication by thewireless terminal from the packet to be relayed by the relay apparatus;calculating and recording a total bandwidth in use used for the radiocommunication by the wireless terminal in the communication area basedon the obtained data; determining an upper limit of a packetretransmission number in accordance with an amount of an availablebandwidth obtained by excluding the total bandwidth in use from amaximum bandwidth available in the radio communication by the wirelessterminal; and retransmitting a packet whose transmission has ended infailure by the relay apparatus, in a range not exceeding the upper limitof the packet retransmission number.
 11. A recording medium storing arelay program for causing a relay apparatus including a computer toexecute processing of relaying a packet to be transmitted in wirelesscommunication by at least one wireless terminal in a communication area,the relay program causing the relay apparatus to execute: packetmonitoring processing of obtaining data on a bandwidth used in radiocommunication by the wireless terminal from the packet to be relayed bythe relay apparatus; bandwidth management processing of calculating andrecording a total bandwidth in use used for the radio communication bythe wireless terminal in the communication area based on the dataobtained in the packet monitoring processing; retransmission adjustmentprocessing of determining an upper limit of a packet retransmissionnumber, in accordance with an amount of an available bandwidth obtainedby excluding the total bandwidth in use from a maximum bandwidthavailable in the radio communication by the wireless terminal; andretransmission processing of retransmitting a packet whose transmissionhas ended in failure by the relay apparatus in a range not exceeding theupper limit of the packet retransmission number determined by theretransmission adjusting processing.